1. Field of the Invention
The present invention relates to an ultrasonic imaging apparatus which detects blood flow data at points in a two-dimensional scanning plane utilizing the Doppler effect and displays a color blood flow mapping image.
2. Description of the Related Art
Let transmitted frequency=f0, received frequency=f1, Doppler-shifted frequency=fd, blood flow velocity=v, sound velocity in living tissues=C, and angle between a beam of ultrasound and a blood vessel=.theta.. Then the received frequency is represented by the equation ##EQU1##
The Doppler-shifted frequency is represented by the equation EQU fd=f1-f0=(2V.multidot.cos .theta./C).multidot.f0 (2)
Using equations (1) and (2) the blood flow velocity is calculated from the Doppler-shifted frequency fd and the angle .theta..
Such a type of ultrasonic imaging apparatus needs the following parameters:
N=the number of transmitting/receiving operations for the same raster (hereinafter referred to as the number of pieces of data); PA1 fr=rate frequency; PA1 P=low-flow-velocity detectability improvement ratio (also called the number of alternate stages), i.e., the number of other rasters on which ultrasound transmitting/receiving operations are performed between the moment that an ultrasound transmitting/receiving operation was performed on a certain raster and the moment that another ultrasound transmitting/receiving operation is performed on the same raster; PA1 fc=cutoff frequency of an MTI filter; PA1 MA=Moving Average; PA1 MAE=Motion Artifact eliminator; PA1 W=angle of field of view; PA1 Lp=raster pitch; PA1 Ln=the number of rasters
With conventional ultrasonic imaging apparatus, an operator is required to adjust these parameters individually, which is troublesome and time-consuming. The adjusted values of those parameters are related with one another, so that the detectable velocity range (the detectable maximum velocity Vmax and minimum velocity Vmin) the operator wants to know truly and the number of frames per second (f/s) will vary. Thus, the operator is required to accumulate the meaning and the interrelation of the parameters as preliminary knowledge. The detectable velocity range and the number of frames per second must be changed according to an imaging region such as abdomen, lower leg, or the like.
For example, the detectable minimum velocity Vmin and maximum velocity Vmax are related to the rate frequency fr, the number of pieces of data N and the number of alternate stages P by the equations EQU Vmin=.alpha..times.((C.times.fr)/(2.times.N.times.P.times.F0.times.cos .theta.)) (3) EQU Vmax=.alpha..times.((C.times.fr)/(4.times.P.times.f0.times.cos .theta.))(4)
where .alpha. is a constant.
Moreover, the number of frames per second f/s is related to the rate frequency fr, the number of pieces of data N and the number of rasters Ln by the equation EQU f/s=.beta..times.(Ln.times.N)/fr) (5)
where .beta. is a constant.
Furthermore, the number of rasters Ln is related to the angle of field of view w and the raster pitch P by the equation EQU Ln=.gamma..times.(W/LP) (6)
where .gamma. is a constant.